Process for inhibiting the polymerization of alpha-chloracrylate esters and the resultant compositions



United States Patent Ofiiice 2,886,494 Patented May 12, 1959 PROCESS FORINHIBITING THE POLYMERIZA- TION OF u-CHLORACRYLATE ESTERS AND THERESULTANT COMPOSITIONS Harry D. Anspon, Easton, Pa., assignor to GeneralAniline & Film Corporation, New York, N.Y., a corporation of Delaware NoDrawing. Application May 1, 1957 Serial No. 656,192

'20 Claims. (Cl. 202-57) This invention relates to improvements in themanufacture, processing and treatment of polymerizable unsaturatedhalogen-containing organic compounds and in particular, tom-chloracrylic acid esters and derivatives thereof. Specifically, thisinvention relates to improvements whereby the handling of such monomericmaterials is facilitated during processing and treatments thereofinvolving the application of heat and other polymerization aids. Y

The esters of a-chloracrylic acid, and particularly the lower alkylesters such as methyl, ethyl, propyl, isopropyl, butyl and the like havebecome increasingly important base materials useful in the manufactureof polymers, which polymers are possessed of outstanding, unusual andunexpected properties. Among the various properties of such polymericmaterials are those outstanding physical properties of high heatdistortion temperature, high flexural and tensile strength, excellentcraze resistance, low notch sensitivity, unique self-extinguishingcharacteristics in burning tests and complete formability which makethese polymers particularly suited for use as a glazing material,especially for the glazing of high-speed aircraft. Among the well knownchemical properties of the monomers from which these polymeric materialsare prepared is the extreme sensitivity and reactivity of the highlypurified monomer to polymerization. In order to prepare a polymersuitable for use as a glazing material and which will be characterizedby the above described advantageous physical properties and, inaddition, have the desirable and absolutely necessary opitcalcharacteristics, it has been discovered that the monomer, before it issubjected to polymerizing conditions to form the final product, must bein an exceptional state of purity otherwise one or several of the abovedescribed physical characteristics will suffer thereby. In addition, ifthe monomer is not handled with the utmost care, and if purification isnot carried out to the utmost degree, there will arise in the finalshaped polymer, or in the polymer subjected to deforming operations inthe making of glazing materials such as canopies and the like, theformation of undesirable color bodies or udesirable bubble formation. Itis thus of paramount importance to conduct the preparation of themonomer under the most stringent of conditions in order to successfullyattain and achieve the utmost in desirable physical and chemicalproperties in the final polymer.

In carrying out the necessary processing involving purification of thevarious monomers contemplated, such techniques as distillations arenecessary. These distillations involve, under the most desirableconditions, the application of considerable quantities of heat to themonomer in order to effect the necessary separation of impurities fromthe monomer. These necessary distillation steps, even when carried outat relatively low temperatures where the pot temperature is of the orderof 50 C., result in rather large losses of the initial charge due to thepremature polymerization of the monomer in the pot. In the absence ofany polymerization inhibitor,

such losses may amount to of the total charge,

or in other Words, processing in the absence of any inhibitor iscompletely worthless and well-nigh impossible if it is desired to obtainpure distilled monomer. With many of the well known inhibitorsheretofore employed with vinyl type or ethylenically unsaturatedmonomers such as hydroquinone, p-tertiary butylcatechol and the like,the results are somewhat improved but not sulficiently to render theprocesses economically feasible. Thus, with tertiary butyl catechol,losses are of the order of 25 to 50% in the pot. Hydroquinone, on theother hand, while a fair inhibitor, contaminates the distilled monomerto the point where, in subsequent polymerization reactions, undesirablecolor formation occurs. In addition, this particular inhibitor, presentas a contaminant, prevents good control of the subsequent polymerizationprocess with many of the desirable polymerization catalysts.

I have discovered that it is possible to process and purify monomers ofm-chloroacrylic acid esters employing distillation techniques involvingthe application of heat to the monomer and at the same time, avoidingany premature polymerization thereof in the pot. In addition, I havediscovered that it is possible to obtain an excellently purified monomerproduct in high yields devoid of any polymerization inhibitorcontaminants, thereby insuring the successful attainment of a shapedpolymer therefrom in subsequent polymerization processes.

It is therefore an object of my invention to provide a new processwhereby monomers of m-chloracrylic acid esters may be processed andhandled without premature polymerization thereof.

It is a further object of my invention'to provide a process wherebyhighly purified monomeric acid esters may be prepared devoid ofcontaminants which interfere with subsequent polymerization thereof. 1

It is still another object of my invention to provide processes for thedistillation of a-chloracrylic acid esters employing heat whereby potlosses due to premature polymerization are minimized.

It is still another object of my invention to provide compositionscomprising monomeric esters of a-chloroacrylic acid which exhibitoutstanding stability towards polymerization.

It is another object of this invention to provide compositionscomprising monomeric esters of a-chloroacrylic acid which exhibitoutstanding and unusual stability against polymerization while under theinfluence of elevated temperatures.

It is a still further object of this invention to provide compositionscomprising monomeric esters of u-ChlOI'O- acrylic acid which exhibitoutstanding and unusual stability against polymerization while under theinfluence of heat radiation.

It is a still further object of this invention to provide compositionscomprising esters of a-chloroacrylic acid which are stable againstpolymerization in the presence of actinic radiation.

Other objects will appear hereinafter as the description proceeds. Theobjects of this invention are achieved by incorporating into themonomeric a-chloroacrylic acid ester, a 1,4-diamino containinganthraquinone compound. The compounds which are contemplated herein mustcontain in the 1- and 4-positions, amino groupings, and may containother substituents in the other substitutable posius. str ctural y, hecontemplated compo nd y be represented as follows:

If; (i). NHR

R; i) NHR4 and leuco forms thereof, wherein R and R may be hydrogen,alkyl, hydroxyalkyl or acyl and R R R R R and R may be amino,substituted amino (for example, alkyl amino, dialkyl amino or acylamino), halo, nitro, alkyl, 'alkoxyl, aryloxy, hydroxy, carboxy,carboxarm'do, carbalkoxy, sulfo, sulfonamido, and substitutedsulfonamido such as alkyl sulfonamido and dialkyl sulfonamido. Among thesuitable compounds which may be used herein are the following:

The amount of the above described compounds which may be employed asinhibitors in the practice ofthis invention will vary considerably andis in no way critical. Ithas, however, been found that amounts fromabout 0.001% up to about 1% thereof based on the weight of themonomerprovide adequate protection to the monomer whereby polymerization isinhibited under the conditions hereinafter to be described.

In order to determine the efficiency of polymerization inhibitors andmake a comparison among the various compounds tested for such inhibitioncharacteristics, the following test procedure was employed. Methyltchloracrylate which had been previously vacuum distilledunderpre-purified nitrogen and which possessed a freezing point'of 36.26C. was poured into 20 mm. outside diameter test tubes on which had beensealed 10 mm. outside diameter necks. These necks were attached toav 2in. length of polyvinyl alcohol tubingwhich could be sealed off with apinch clamp. The test tube had,pre-.

viously been coated with a solution of polyvinyl alcohol.

and Congo red. This solution, on drying, deposited a red film over theglass through which observation of the contents of the tube could bemade, but which would filter out light of the wave lengths responsiblefor polymerization. Each of thesetubes holds approximately 33 ml. ofmonomer when filled up to the neck at the point where the polyvinylalcohol tubing isattached. The compounds to be tested for inhibitingcharacteristics are weighed-into each tube prior to the addition of themon- Other and each tube swept with prepurified nitrogen.

After adding the monomer to the tube, the polyvinyl.

alcohol tubing is pinched shut so that no air may contact the liquidmonomer present below the pinch clamp. The tubes are then sealed off andplaced on a large mixing wheel which rotates at 3 revolutions perminute. The following heating cycle is employed in the test procedure:

4 days at '20-25" C.

5' hrs. at,50 C.

10 days at 20-25 C.

19 hrs. at -40 C.

3 days at -50 C.

5 days at 60 C.

Remainder of time at -70 C.

Each of the tubes on the mixinghwheel is observed to determine the timerequired to gel or to form a nonflowing polymer in the tube whilerotating at 3 revolutions per minute. Employing the above describedtesting procedure, the followingmaterials WSI'ByUSEdfOI". each 33 ml. ofmethyla-chloracrylate monomer:

0.04 g. 2-methyl anthraquinone 0.04 g. 2,3'-dimethyl anthraquinone 0.04'g. 1#amino-2,3-dimethyl anthraquinone 0.04 g. 1,5 -diamino anthraquinone0.04 g. 1-amino-4-hydroxy anthraquinone 0.04 g. Z-amino anthraquinone0.04 g. thioureav 0.04 g. copper powder I 0.04 g. phenol 0.04-g.p-tertiary butyl catechol 0.04 g. sulfur 'Ihejpure: monomer with noadded inhibitor was found.-

to require 28 days to'gel; in the above described test procedure. Themonomer; containing copper powder gelled in 3'days 4hrs., thosecontaining the l,5-diarninoanthraquinone and Z-methyl anthraquinone in10 days,v those; containing the 1-arnino-4-hydroxy anthraquinone,

the.2,3-dimethyl anthraquinone, the 1-amino-2,3-dirnethyl anthraquinone,and the thioureav in less than 20 days,.

and with phenol and Z-amino anthraquinone in 27 days. Each of thesematerials, thus, it will be observed, while heretofore described asvinyl type polymerization inhibitors, actually, with the monomerscontemplated in thisinvention, instead of being inhibitors of thepolymer ization reaction, appeared to catalyze it. The-p-tertiary' butylcatechol, on; theother hand, and sulfur gavesome what better results,the. former requiring, 3-2 days and the latter 28-days. The sameprocedure employing 0.04. g..

of the compounds ofthis invention do not produce any gelling from about50 to days. It will thus be observed thateach of the. compoundscontemplated herein is, an excellentvinhibitor for the monomers, ofa-chloro-- acrylic acid esters and unexpectedly superior to othersubstituted, anthraquinones lacking a 1,4-diamino substituent. Inaddition,,these compounds are, far, superiorv to innumerable, otherswhich have heretofore been considered satisfactory inhibitors for vinylor ethylenically.

unsaturated. monomers.

The, following examples will serve. to illustratethe;

unexpected and outstanding benefits; to, bederived. from: thezuse of theinhibitors of this invention, which have been described above.

Example 1 eration' undera vacuum of 30 mm. of mercury employingpottemperatures during the distillation ranging fi'om about 58 to-63 C.The recovery-'ofpurifi'ed monomer: amounts to 967 ml. and this producthas a freezing point of T-36-67' C., which represents a product having apurity of better than 99%. a

Example 2 The procedure of Example 1 is repeated except that theinhibitor employed is p-tertiary butyl catechol in the same amounts.Recovery from this procedure is 571 ml. of monomer having a freezingpoint of '"36.77' C.

Example 3 i Example 4 To a charge of 1000 ml. of methyl-u-chloroacrylatecontained in a flask there are added 1.0 g. of the inhibitor used inExample 1 and 0.4 g. of chloranil. The latter compound is employed toinhibit and reduce the tendency for the subject monomer to polymerizeoutside of the still pot, and especially where the monomer is subjectedto elevated temperatures for long periods of time, such as in anextended reflux operation. The use of chloranil for such purposes isfully described in my copending application Serial No. 649,305, filedMarch 29, 1957. In this experiment the monomer employed has a freezingpoint of 37.15 C. The flask, after charging, is provided with a packedcolumn of 30 in. in height and then the entire system is swept andsubsequently maintained under nitrogen. Distillation is then carried outunder a vacuum of 30 mm. of mercury employing a pot temperature rangingfrom about 59 to 62 C. The take-off from the reflux column is adjustedso that the total reflux time is 12 hrs. At the end of this period oftime there is recovered 986 ml. of highly purifiedmethyl-achloroacrylate monomer which has a' freezing point of 36.48" C.This procedure demonstrates the increased efiiciency of distillation andyield of monomer wherein advantage is taken of the inhibitingcharacteristics of chloranil in the still column. Since an efiicientfractionation employing such reflux columns makes possible the recoveryof a more highly purified monomer product, it is desirable to operate inthis manner and therefore it is advisable to employ the additionalinhibitor which gives protection against polymerization outside of thestill pot.

Eample 5 The procedure of Example 1 is again repeated employinghydroquinone as the inhibitor. In this case, only 610 ml. of purifiedmonomer is recoverable from the original charge of 1 liter. The residuein the still pot is substantially fully polymerized monomer.

Example 6 The procedure of Example 1 is again repeated employing as theinhibitor 1.2 g. of 1,4-bis(methylamino) anthraquinone. The recovery inthis case amounts to 960 ml. of monomer.

the inhibiting compounds 1-amino-4-hydroxy anthracase polymer plugsbeing evident in the ,7 Example 8 v p The procedure of Example 1 isagain repeated using ds the inhibitor 1,4-diamino anthraquinone. coveryis achieved, amounting to 959 ml.

Example 9 The procedure of Example 1 is once again repeated using as theinhibitor 1.2 anthraquinone. Excellent recovery of monomer is obtained.

Examples 10-12 Repeating the procedure of Example 1 employing'asinhibitors, however, with different batches of monomer,

1,4-diamino-5-nitro anthraquinone, 1,4,5,8-tetraamino an thraquinone,and 1,4-diarnino-5,8-dihydroxy anthraquinone, results in each instancein an excellent recovery of better than of the original charge of ahighly puriled monomer characterized by a purity of better than 99.5%.

Example 13 The procedure of Example 1 is repeated employing 1.2 g. of1,5-diamino anthraquinone. Recovery amounts to only 410 ml. of monomerand the remaining contents of the still pot are completely set up.

Example 14 The procedure of Example 4 is repeated employing as quinoneon the one hand and with a second charge of 1-amino-2,3-dimethylanthraquinone. In each case, less than 300 ml. of monomer isrecoverable, the remainder being completely set up in the still pot, andalso in each fractionation column, requiring shutdown.

The above examples demonstrate not only the outstanding and improvedinhibiting characteristics of the compounds with which this-invention isconcerned, but

they also demonstrate that similar compounds not encompassed herein andwhich showed up poorly in the test procedure described above forevaluating inhibitors, were equally poor in actual practice.

While the invention has been described in the specific examples inconnection with methyl-u-chloroacrylate, it is also applicable to othera-halogen substituted acrylic compounds. Thus, in addition to the alkylesters of a-chloroacrylic acid such as ethyl, propyl, butyl esters andother aliphatic and aromatic esters such as phenyl, benzyl, cyclohexyl,allyl, methallyl, and the like, the corresponding a-bromo and u-fluoroacrylic acid esters may be employed. Also, the polyhydric alcohol esterssuch as the glycol di-a-chloroacrylate may be used.

Variations and modifications which will be obvious and apparent to thoseskilled in the art may be made in the procedure above described withoutdeparting from the scope and spirit of my invention.

I claim:

1. A composition comprising a liquid monomeric a-haloacrylic acid esterof an alcohol and a polymerizing inhibiting amount of a 1,4-diaminocontaining anthraquinone compound.

2. A composition comprising a liquid lower alkyl ester of.OL-ChIOI'OaCI'YIiC acid and a polymerizing inhibiting amount of a1,4-diamino anthraquinone compound.

3. A composition comprising a monomeric methyl-mchloroacrylate and apolymerization inhibiting amount of a 1,4-diamino containinganthraquinone compound.

4. A composition comprising a monomeric methyl-achloroacrylate and atleast about 0.001% by weight based on the weight of the said monomer ofa 1,4-diamino anthraquinone compound.

5. A composition as defined in claim 4 wherein the anthraquinonecompound is 1,4-diamino anthraquinone.

Excellent reg. of 1,4-diamino-2-methoxy.

6. A composition as defined" in claim 4 wherein the n hraquinone ompoundaminQ-A-m thYIam nO anfl mli inone- 7. A 'composition as definedjnclaim; 4 wherein the. anthraquinone compound is 1,4-bis(methy1amino)anthraquinone.

8.. A composition as, defined in claim 4- wherein the anthraquinonecompound is lA-diamino-S-nitro anthraql inone;

9'. A composition as defined in claim 4 wherein the anthraquinonecompound is 1,4-diamino-5,8-dihydroxyanthraquinone.

10. A process for inhibiting the polymerization ofa liquid a-haloacrylieacid ester which comprises incor porating therewith a 1,4-diamino,containing anthra quinonee 11.. A process for inhibiting the.polymerization of monome i e hyl-ehl roa y te:whi h omprinc.orporatingtherewith about 0.001%v to about, 1% by weight based onthe weight of the monomer of a.-1,4- diamino containing anthraqninone.

12. A process for inhibiting the polymerization of monomericmethyl-a-chloroacrylate which comprises adding thereto about 0.1%' byweight based on the weight of' the monomer ofa methylated 1,'4-'aminocontaining anthraquinone compound;

13. A process for inhibiting the polymerization of monomericmethyl-u-chloroacrylate which comprises adding. thereto aboutv 0.1% byweight based. on the weight of the monomer: of. 1-amino-4-methylaminoant r qu no e- 14. A process. monomeric methyl-a-chloroacrylate whichcomprises adding thereto. about, 0.1% by weight based on the. weight ofthe, monomer of 1,4.-bis(methylamino)anthraquinone.

15. In a process where monomeric methyl-a-chloro-.

acrylate is subjected to elevated temperatures, the. step of inhibitingpolymerization by the presence of a 1, 4 diaminQ: containing anthraqinone" in contact with. the

ester.

for inhibiting the polymerization of 16. A process for purifyingmethyl-a-chloroacrylate which comprises distilling saidester inthepresence ofi-E a polymerization inhibit ng. mount of a 1,4-diaminoanthraquinone compound incontact with the ester.

. 17*. In 1 the; distillation of: methyl,-a-chloro.a.crylate,vv theimprovement which: comprises: conducting, said distillationin the,preseneeiofi a; polymerization inhibiting amount: of 1,4-diamino.containing-.anthraquinone. compound in contact with the ester. 7

18. In the distillation'of monomeric methyl-a-chloroacrylate, theimprovement which comprises conducting thev distillation in the.presence of..abou.t 0.1% by. weight based, onthev weight of the monomerof a methylated.

1,4-diamino containing anthraquinone in contact with the ester.

19. A process. for purifying a. liquid monomeric u-haloacrylic, acid.ester, which comprises distilling said ester. in.

the presence of a polymerization inhibiting amount of a.1,4-diarninoanthraquinone compound in contact with the ester.

20. In the distillation of liquid monomeric a-haloacrylic acid ester,the -improvement-Which comprises conducting said distillation in thepresence of a polymerization-inhibiting amount of 1,4-diamino containinganthraquinone compound in contaet with the ester.

References Gited in the file of this patent UNITED STATES PATENTS2,233,835. Craiizfordetv a1. .Mar. 4,1941 2,241,770 Dreisbacket al. May13,1941 2,388,041 Craig Oct. 30, 19.45. 2,399,340. Franz Apr. 30, 19462,407,861 Wolk Sept. 17, 1946 2,476,528 Barnes July 19, 1949. 2,694,726Anspon' Nov. 16, 1954 2,704,770 Anspon Mar. 22, 1955..

FOREIGN PATENTS 528,761. Great Britain Nov. 6', 1940? 750,358 GreatBritain. June 13', 1956

18. IN THE DISTILLATION OF MONOMERIC METHYL-A-CHLOROACRYLATE, THEIMPROVEMENT WHICH COMPRISES CONDUCTING THE DISTILLATION IN THE PRESENCEOF ABOUT 0.1% BY WEIGHT BASED ON THE WEIGHT OF THE MONOMER OF AMETHYLATED 1,4-DIAMINO CONTAINING ANTHRAQUINONE IN CONTACT WITH THEESTER.